When I talk about "murderhobos vs mercenaries" I'm talking about characters for whom the majority of their existence (say, 75%) is based around a lifestyle of killing on whimsy vs a lifestyle of profit via death.
OK, got that.
And from there I'm having trouble parsing the following as a group, so I've lobbed in some questions:
Well, considering I'm speaking from what I've experienced as a DM who doesn't run evil campaigns, and a player who doesn't play in evil campaigns, I certainly have not witnessed people playing a "murderous campaign" or an "evil campaign". So, I'd appreciate it if you wouldn't tell me I don't know what I'm looking at or playing in, because I'm certainly not telling you or anyone else that their own experiences are incorrect.
The singular evil campaign I do run (my Drow campaign I've mentioned before) I an incredibly picky with my players because while murder may be a regular part of life in the Underdark, it is most decidedly not a murderhobo campaign.
So...er...you run an evil campaign but you won't let the PCs be, by your definition, evil?
Doesn't make sense, somehow.
I separated whimsy from XP acquisition for a reason. The delineation is important.
I don't think I'm reading this right, because to me it says that killing for whimsy (as defined above) is not OK but killing for xp acquisition is.
What's the difference - particularly to those classes that gain xp via killing (e.g. any version of Assassin)?
Every party wants XP and loot. Every. Last. One.
Murderhobos get it by killing anything that walks, talks or gets in their way.
Mercanries get it by accepting contracts to kill specific things.
Holy Crusaders get it by killing things that are specifically unholy.
and so on and so forth.
You've said you won't run a murderhobo campaign. What about a mercenary campaign, or a holy crusader campaign?
It seems to me (and please correct me if I'm wrong) you're somewhat saying murderhobos have to be by definition chaotic evil, or close. Yet I'd hazard a guess we've all seen or run or DMed campaigns where characters of all alignments operate largely under a murderhobo ethic once they get into the field and it's them or us.
While murderhobos may have the lowest bar, the bar is so low that there is little differentiation in the mind of a murderhobo between something that gives XP and loot and something that is simply killable.
"Something that is simply killable" may still have loot and still give xp, until and unless you as DM houserule that it doesn't.
I also wonder if you're being a bit harsh with the term murderhobo in the first place. I certainly don't see it as meaning "psychotic bloodthirsty killer who most civilizations would lock away never to be seen again", yet that seems to be the level of revulsion you have for them.
I mean, hell, Thorin Oakenshield's party in The Hobbit were by and large murderhobos - they had no home, and they sure did some killing now and then. But they - or at least Thorin - didn't turn evil until they'd got their home back; and even that didn't last. Ditto the main Party in LotR - between the time they leave Rivendell and the crowning of Aragorn they're pretty much - you guessed it - murderhobos. And there's a whole lot of Orcs who would agree, were they still alive to do so.
Lan-"by the time Pippin and Sam got to Mt. Doom they'd become mordorhobos"-efan